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and water were employed. During this period he began a friendly correspondence with Kepler, which continued until the death of the latter; and about the same time appeared a treatise on the sphere after the Ptolemaic system, which has been attributed to Galileo on rather insufficient grounds. It was published from a MS. in the library of Somaschi at Venice (Rome, 1656). Probably between the years 1593 and 1597 Galileo became a convert to the Copernican theory of the revolution of the earth about the sun; but it is impossible to fix the date of this important event in his life, for he says in a letter to Kepler (1597), that in deference to public opinion he did not declare his conviction of the truth of the new doctrines for some years after he had formed it. On the expiration of the term of his professorship the Venetian senate appointed him for six years more, and raised his salary to 320 florins. In 1604, a new star of remarkable brilliancy having appeared in the constellation Serpentarius, he attacked the popular notion that it was a meteor, and proved by the absence of parallax that it was far beyond the limits of our system. His appointment at the university was again renewed, with an addition of 200 florins to his salary. The crowds that came to hear him were now so great that he was sometimes obliged to lecture in the open air. In 1609 a report reached him at Venice that a Dutchman had constructed an instrument which had the property of making distant objects seem near. On his return to Padua the philosopher immediately applied himself to the solution of the mystery, and, after trying several combinations of lenses, succeeded in making an instrument which magnified three times. It consisted merely of a leaden organ pipe, with a plano-convex glass at one end and a plano-concave at the other. This he carried to Venice, where it at once became an object of the intensest public curiosity. He presented it to the senate, who thereupon confirmed him in his professorship for life, and raised his salary to 1,000 florins. Galileo soon constructed another telescope which magnified eight times, and at length a third which had a power of 30. The wonders of the heavens now unfolded to him, which no man had ever seen before, filled him with “incredible delight.” His earliest observations were upon the moon, whose inequalities of surface he was the first to trace. He saw myriads of stars in the milky way, counted 40 in the Pleiades, and at length, on Jan. 13, 1610, after six nights' observation, discovered the revolution of four satellites around the planet Jupiter. He did not publish this intelligence until by repeated examination, up to March 22, he had insured himself against the danger of mistake. The account of his discoveries, which he entitled Sidereus Nuncius, the “Sidereal Messenger,” was received by the astronomers of the old school with insults and incredulity. Some exclaimed against the impiety of scooping out valleys from the fair face of the moon; some attempted to explain away the satellites of Jupiter as mere appearances caused by reflected light. A professor in the university of Padua argued that as there were only seven metals, seven days in the week, and seven apertures in a man's head, so there could be but seven planets; and when forced to admit the visibility of the satellites through the telescope, he reasoned that, being invisible to the naked eye, they were useless, and consequently did not exist. Several persons claimed a prior discovery of the “Jovian planets,” and the astronomer Zach, as late as 1788, claimed for Thomas Harriot the credit of having observed them on Jan. 16, 1610, some time before Galileo's discovery was made known. According to Sir David Brewster, however, Harriot did not see them till Oct. 17. Viviani, in his life of Galileo, tells us that the telescope led him to the construction of the compound microscope, and that he presented one to the king of Poland. The grand duke of Tuscany gave Galileo 1,000 florins, and made him his philosopher and mathematician with a liberal salary and nominal duties. He now removed to Florence. To guard against future attempts to steal his laurels, he published his subsequent discoveries in enigmas, and thus in the course of the same year he announced that Saturn was “triple,” an appearance which Huygens subsequently showed was caused by that planet's rings. Galileo was the first to notice that Venus exhibits phases like those of the moon; and if not the first to descry spots on the sun's disk, he was at least the first to note their peculiarities, and to infer from them the sun's rotation. Some of these observations were made in 1611 at Rome, which he then visited for the first time, where he erected his telescope in the Quirinal garden belonging to Cardinal Bandini. He was received with the highest honors, and became a member of the famous Lincean academy. In 1612 he combated in his work on the laws of floating bodies the common opinion that the tendency of substances to sink or swim in water depends on their shape. With this period in his life the philosopher may be said to have reached the zenith of his prosperity, while at the same time the malice of his enemies began to acquire a dangerous intensity. The Copernican system, which he had long taught in public, afforded a good pretext for attacking him. The sun's revolution round the earth was thought to be a truth of Scripture. Certain Tuscan ecclesiastics began to preach against the wickedness of sending our world spinning through space, and a sarcastic Dominican hurled a sermon at Galileo from the text: Viri Galilæi, quid statis adspicientes in cœlum? “Ye men of Galilee, why stand ye looking up into heaven?” In 1613 Galileo addressed a letter to his pupil Castelli, showing that the language of the Bible should be interpreted according to popular ideas, and that the Ptolemaic system is really as much at variance with it as the Copernican.